Influence of Fuel Nuclide Composition and Neutron Spectrum on Reactor Pressure Vessel Dosimetry

This study examines how common simplifications used in reactor dosimetry calculation models affect the accuracy of the resulting responses. In particular, it focuses on the treatment of fuel composition and the modelling of the neutron source spectrum . In actual reactors, fuel assemblies (FAs) operate at a wide range of burnup levels. Modelling each FA with its specific isotopic composition is generally impractical; therefore, dosimetry models commonly assume fresh‑fuel compositions for all assemblies. Similarly, because each FA may produce fission neutrons with a slightly different due to burnup effects, an additional simplification is often applied in which only a single, averaged is used for the entire core. To evaluate the impact of these simplifications, we selected the BALAKOVO‑3 VVER‑1000 benchmark from the SINBAD database. The results show that dosimeter responses behind the reactor pressure vessel (RPV) exhibit very high sensitivity to the choice of , whereas they are almost unaffected by replacing burnt‑fuel compositions with the fresh‑fuel approximation. This finding fully justifies the widespread use of fresh‑fuel compositions in reactor dosimetry models. However, it also highlights the need for special attention to the selection of the source spectrum, which should represent the actual reactor conditions as closely as possible. All calculations were performed using the MCNP6.3.0 and SCALE/TRITON 6.3.1 codes.